The present invention relates to pseudospark discharge devices and methods, and more particularly to a coaxial pseudospark power switch having a compact, coaxial configuration that provides a pseudospark discharge at a plurality of discharge locations upon being triggered from an on-axis trigger location.
The breakdown voltage between two parallel plane electrodes is a function of the product of the distance d between the electrodes and the gas pressure p in the region between the electrodes. This voltage is described by the well-known Paschen curve, presented below, which curve shows similar behavior for all kinds of gases.
For special geometries, i.e., spaced apart planar electrodes having an aligned central hole, it has been shown that a different type of discharge exists in the region on the Paschen curve between the Paschen minimum and the vacuum breakdown. This discharge is characterized more as a glow rather than an arc, and is referred to as a "pseudospark". See, e.g., Frank, et al., "The Fundamentals of the Pseudospark and Its Applications,", IEEE Transactions on Plasma Science, Vol. 17, No. 5, pp. 748-53 (October 1989).
A pseudospark discharge switch is a discharge device that provides a diffuse plasma discharge, i.e., a pseudospark, between two planar electrodes having an aligned central hole immersed in a low pressure gas environment. The low pressure gas environment assures operation on the left side of the Paschen curve. Triggering of the pseudospark switch is controlled by any suitable mechanism that increases the charge carrier density in the region of the electrodes. If triggered electrically, a pseudospark device is typically referred to as a pseudospark switch. If triggered optically, a pseudospark device is sometimes referred to as a back-lighted thyraton (BLT). As used herein, the terms "pseudospark" or "pseudospark switch" are intended to refer to any type of diffuse discharge device operating on the left side of the Paschen curve, regardless of how the device is triggered.
The main advantage of the pseudospark discharge device is its ability to rapidly switch large currents at high voltages in a low pressure gas environment. Thus, the pseudospark discharge switch can be used to replace triggered gas gap breakdown switches, rotating arc switches, and other high current switching devices.
Further, because the pseudospark discharge represents a very rapid breakdown phase, the discharge operates with an anomalously high cold-cathode emission, which is much higher than the emission from a standard hot cathode. Thus, in addition to high power switching applications, the pseudospark discharge switch may be effectively used: (1) as a source of high-density beams of electrons, see Bloess et al., "The Triggered Pseudospark Chamber as a Fast Switch and as a High-Intensity Beam Source," Nucl. Instrum. Methods, Vol. 205, p. 173 (1983); (2) as a source of high-density beams of ions, see Bauer et al., "High Power Pseudospark as an X-ray Source," Proc 18th Int. Conf. on Phenomena in Ion Gases (Swansea, U.K.), pp. 4-718 (1987); (3) to generate laser radiation, Christiansen et al., "Pulsed Laser Oscillation at 488.0 nm and 514.5 nm in an Ar-He Pseudospark Discharge," Optics Comm., Vol. 56, No. 1, p. 39 (1985); (4) to generate microwaves, J. Gundlach, "Microwave-excitation by a Pseudospark Electron Beam" (in German), Master thesis, Physics Institute, University of Duesseldorf, Duesseldorf, FRG (1986); and (5) to generate short duration X-ray flashes, P. Roehlen, "The Pseudospark Discharge as an Intense Source of Electron Beams" (in German), Master thesis, Physics Institute, University of Duesseldorf, Duesseldorf, FRG (1985).
In order to increase the discharge capacity of a pseudospark device, it is known in the art to construct a multigap pseudospark chamber, comprising stacked spaced-apart electrodes having central holes, as shown, e.g., in the Frank et al. reference cited above. It is also known in the art to connect two or more pseudospark devices in parallel, or to make a multichannel pseudospark (MUPS) switch (which is effectively the equivalent of parallel-connected pseudospark switches sharing a common cathode and anode plate), as taught, e.g., in Mechtersheimer et al., "Multichannel Pseudo-Spark Switch (MUPS)," J. Phys. E: Sci. Instrum., Vol. 20, pp. 270-73 (1987).
Unfortunately, multi-gap pseudospark devices, MUPS switches, or a network of pseudospark discharge switches connected in parallel, occupy a relatively large volume. Further, a network of parallel pseudospark devices requires a rather sophisticated trigger mechanism and control circuit in order to assure that all of the pseudospark switches are triggered at the same time. Thus, despite the numerous advantages and versatility of the pseudospark discharge device, there remains a need in the art for a more compact pseudospark discharge geometry that has the same or higher discharge capacity as the larger volume multichannel or parallel-connected pseudospark discharge devices, and that is easily triggered using a single trigger control signal.
Moreover, all pseudospark switch geometries must use some sort of insulator in order to separate the anode from the cathode. If this insulator is near the discharge path, i.e., in the vicinity of the aligned hole of the electrodes, then it is possible that discharge products may accumulate on, and hence eventually coat, the insulator, thereby adversely affecting its insulative properties and degrading switch performance. What is also needed, therefore, is a pseudospark switch geometry that prevents discharge products from accumulating on the electrode insulator.
Further, a pseudospark switch design of low inductance is needed in order to allow large currents to be switched at high speed.
The present invention advantageously addresses the above and other needs.